The present invention relates generally to optical lithography techniques used in semiconductor device processing and, more particularly, to a method for correction of defects in lithography masks.
Semiconductor fabrication techniques often utilize a mask or reticle in a conventional lithographic system to project an image onto a semiconductor wafer, wherein radiation is provided through (or reflected off) the mask/reticle, and passed through a focusing optical system to form the image (e.g., an integrated circuit pattern). The semiconductor wafer is positioned to receive the radiation transmitted through (or reflected off) the mask/reticle such that the image formed on the wafer corresponds to the pattern on the mask/reticle. The radiation source may be light, such as ultraviolet light, vacuum ultraviolet (VUV) light, extreme ultraviolet light (EUV) and deep ultraviolet light (DUV). In addition, the radiation may also be x-ray radiation, e-beam radiation, etc. Generally, the formed image is utilized on the wafer in order to pattern a layer of material, such as a photoresist material. The photoresist material, in turn, may be utilized to define doping regions, deposition regions, etching regions, or other structures associated with the manufacture of integrated circuits (ICs).
Existing photolithography masks (e.g., leading edge masks) are fabricated at a significant cost and lead-time. One of the most significant cost factors in mask production is the desire for producing completely defect free masks, since a non-repairable defect (or a requirement to implement even a slight design change) may result in the need to create an entirely new mask. In addition to the added direct cost, fabricating a new mask can delay product qualification, thus resulting in even greater economic loss.
Unfortunately, producing a mask without printable defects is one of the difficult challenges in mask manufacturing. Although meeting critical dimension (CD) control and image placement accuracies are also difficult challenges, producing a mask with no printable defects arguably remains the most difficult due to factors such as smaller feature spacing, smaller defect criteria and a need for minimal transmission loss in a repaired area, and increases in the complexity of optical proximity correction (OPC). Such stringent requirements are driven by the necessity of the low-k1 factor of leading-edge lithography. With the continued extension of existing 248 and 193 nm wavelengths, as well as the delay of 157 nm lithography, low-k1 lithography will continue as the dominant lithography technique for the foreseeable future. As a direct result, the use of both OPC and embedded and alternating aperture phase shift mask (PSM) usage will increase for quite some time. With these requirements comes a stronger need for mask repair that is both robust and cost-effective.